3 ms·
FYI most rocks come in at less than 3 tonnes per cubic meter, around 2.5-3. It’s quite rare for in situ rock to have a unit weight (density I guess?) higher tha
by abduhl 3y ago
FYI most rocks come in at less than 3 tonnes per cubic meter, around 2.5-3. It’s quite rare for in situ rock to have a unit weight (density I guess?) higher than this.
I don’t know where you’re getting this fun fact either. It’s very rare for a building to weigh as much as its excavated footprint absent an intentional design. The Empire State Building uses deep foundations as far as I’m aware, indicating that it weighed more than its excavated footprint.
The prevalence of deep foundations throughout New York also explains why this paper is not good: it assumes and applies a uniform surface pressure across the city, without consideration for foundation system.
- gcanyon 3y agoI don’t know where I’m getting this fun fact either; I read this <somewhere> at least twenty years ago, used it to succeed at the Fermi problem maybe ten years ago.
- ghc 3y agoBased on publicly available information: The estimated weight of the building is: 365,000 tons The foundation area of the building is: 79,288 sq. ft. The foundation was laid at a depth of: 55.66 ft. The estimated density of removed rock: 165 lbs / cu. ft. The calculated weight of removed rock: 364086.5 tons It's very close actually!
- gcanyon 3y agoThanks for this; I read this a long time ago and have no clue where, so it’s nice to have the backup of some math.
- abduhl 3y agoThis is footprint. It’s unclear whether the full footprint was sunk to your depth. Regardless, that’s much closer than I anticipated it would be, which is pleasantly surprising. We can refine the estimate as well: surface soils probably make up half of the depth (25 ft) and granite rock the other half (30 ft). Blended unit weight would then be ~150 pcf. About 327,000 short ton.
- ghc 3y agoI based my estimate on photos of the foundation work like: https://keithyorkcity.files.wordpress.com/2013/02/1930-march-31-looking-se.jpg https://keithyorkcity.files.wordpress.com/2013/02/1930-march... I couldn't find actual blueprints.
- SoftTalker 3y agoI'm not sure that surface soil is that deep. I seem to recall that in parts of central park the granite is exposed.
- saalweachter 3y agoYeah, NY throughout the Hudson Valley has shallow soil. The glaciers swept everything clean 21k years ago, dropped it all to form Long Island, and barely any of it has come back. (Looking it up, the first result says that soil for at a rate of about 0.5-1 inch/millennia, which sounds about right for how much has re-accumulated, on average.)
- 082349872349872 3y agoAn anecdote that I've heard is that the NYC skyline and underlying geologic map correlate pretty closely; the skyscrapers were apparently built where the bedrock was conveniently close to the surface.